What's already known about this topic? Megalencephaly-capillary malformation (MCAP) syndrome is a rare disorder characterized by growth dysregulation, central nervous system and vascular anomalies, and distal limb malformations. Disruption of PI3K-AKT signaling has recently been implicated as the cause of MCAP. What does this study add? This study reports a case of MCAP with bilateral pleural effusions and fetal hydrops managed with thoracoamniotic shunt placement, highlights characteristic features of MCAP that may facilitate prenatal diagnosis, and discusses the possibility of prenatal molecular diagnosis in future cases.